U.S. patent application number 10/278179 was filed with the patent office on 2003-12-04 for metal nitride formation.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Byun, Jeong Soo, Gelatos, Avgerinos V., Jackson, Robert L., Mak, Alfred W., Thakur, Randhir P.S., Xi, Ming, Yoon, Hyungsuk Alexander, Zhang, Hui.
Application Number | 20030224217 10/278179 |
Document ID | / |
Family ID | 29586495 |
Filed Date | 2003-12-04 |
United States Patent
Application |
20030224217 |
Kind Code |
A1 |
Byun, Jeong Soo ; et
al. |
December 4, 2003 |
Metal nitride formation
Abstract
A process for treating refractory metal-boron layers deposited
by atomic layer deposition resulting in the formation of a ternary
amorphous refractory metal-nitrogen-boron film is disclosed. The
resulting ternary film remains amorphous following thermal
annealing at temperatures up to 800.degree. C. The ternary films
are formed following thermal annealing in a reactive
nitrogen-containing gas. Subsequent processing does not disrupt the
amorphous character of the ternary film. arrangement where a
blended solution is supplied to a remote point of use.
Inventors: |
Byun, Jeong Soo; (Cupertino,
CA) ; Mak, Alfred W.; (Union City, CA) ;
Zhang, Hui; (Santa Clara, CA) ; Yoon, Hyungsuk
Alexander; (Santa Clara, CA) ; Gelatos, Avgerinos
V.; (Redwood City, CA) ; Jackson, Robert L.;
(San Jose, CA) ; Xi, Ming; (Palo Alto, CA)
; Thakur, Randhir P.S.; (San Jose, CA) |
Correspondence
Address: |
PATENT COUNSEL
APPLIED MATERIALS, INC.
Legal Affairs Department
P.O. BOX 450A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
29586495 |
Appl. No.: |
10/278179 |
Filed: |
October 21, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60384641 |
May 31, 2002 |
|
|
|
Current U.S.
Class: |
428/698 ;
257/E21.021; 257/E21.171; 428/469 |
Current CPC
Class: |
C23C 16/45525 20130101;
H01L 21/28562 20130101; H01L 28/75 20130101; H01L 21/76846
20130101; H01L 21/76856 20130101; H01L 21/76864 20130101; C04B
2235/421 20130101; C23C 16/38 20130101; C04B 35/58007 20130101;
C23C 16/56 20130101 |
Class at
Publication: |
428/698 ;
428/469 |
International
Class: |
B32B 018/00 |
Claims
1. A process for formation of a nitrogen-containing refractory
metal film comprising the steps of depositing a refractory
metal-boron layer on the substrate; and annealing a substrate in a
nitrogen-containing atmosphere at a temperature of at least
400.degree. C.
2. The process of claim 1 wherein said refractory metal-boron layer
is deposited by atomic layer deposition.
3. The process of claim 1 wherein said refractory metal-boron layer
comprises more than one refractory metals.
4. The process of claim 1 wherein the one or more refractory metal
is selected from the group of tungsten (W), titanium (Ti), tantalum
(Ta), molybdenum (Mo), zirconium (Zr), hafnium (Hf), cobalt (Co),
ruthenium (Ru), platinum (Pt), iridium (Ir), palladium (Pd) or
combinations thereof.
5. The process of claim 1 wherein said nitrogen-containing
atmosphere comprises one or more gases from the group of ammonia,
hydrazine, derivatives of hydrazine or nitrogen gas.
6. The process of claim 1 wherein said nitrogen-containing
atmosphere comprises one or more gases from the group of ammonia,
hydrazine, derivatives of hydrazine or nitrogen gas which has been
activated by a plasma.
7. The process of claim 1 wherein the annealing step is performed
at a temperature in a range from about 400.degree. C. to about
500.degree. C.
8. The process of claim 1 wherein the annealing step is performed
at a temperature in a range from about 500.degree. C. to about
800.degree. C.
9. The process of claim 1 wherein the annealing step is performed
for a time in a range of about 10 seconds to about 100 seconds.
10. A process for treating a substrate on which a tungsten-boron
layer has been deposited comprising the step of annealing said
substrate in the presence of ammonia ambient.
11. The process of claim 10 wherein the annealing step occurs at an
ambient temperature between about 400.degree. C. and about
500.degree. C.
12. The process of claim 10 wherein the annealing step occurs at an
ambient temperature between about 500.degree. C. and about
800.degree. C.
13. A process for forming a device, comprising the steps of:
depositing a refractory metal-boron layer on a substrate having a
dielectric layer thereon, wherein the dielectric layer has one or
more via holes therein; and annealing the substrate in a reactive
nitrogen-containing gas.
14. The process for forming a device of claim 20 further comprising
the step of depositing a conductive layer on the substrate, wherein
the conductive layer fills said via holes.
15. The process of claim 13 wherein the refractory metal-boron
layer is tungsten boride.
16. The process of claim 13 wherein the reactive
nitrogen-containing gas is ammonia.
17. The process of claim 14 wherein the conductive layer is
copper.
18. A process for fabrication of a MIM structured capacitor
comprising the steps of: depositing a refractory metal-boron layer
on a substrate having a dielectric layer thereon and having a
storage node communicating through a portion of said substrate,
wherein the dielectric layer has a via hole therein and wherein a
top surface of said storage node communicates with said via hole;
and annealing said substrate in a reactive nitrogen-containing
gas.
19. The process for fabrication of a MIM structured capacitor of
claim 18 further comprising the step of depositing a high
dielectric constant insulator on the substrate.
20. The process for fabrication of a MIM structured capacitor of
claim 19 further comprising the step of depositing an upper
electrode layer on said substrate, said upper electrode layer
filling said via holes.
21. The process of claim 18 wherein the refractory metal-boron
layer is tungsten boride.
22. The process of claim 18 wherein the reactive
nitrogen-containing gas is ammonia.
23. The process of claim 26 wherein said high dielectric constant
insulator is tantalum dioxide.
24. The process of claim 20 wherein said upper electrode layer is
titanium nitride.
25. An interconnect device comprising: (a) a substrate having a
dielectric layer thereon, wherein the dielectric layer has one or
more via holes therein; (b) a refractory metal-nitrogen-boron layer
deposited on said substrate; and (c) a conductive layer on said
substrate overlying said refractory metal-nitrogen-boron layer and
wherein said conductive layer fills said via holes.
26. The interconnect device of claim 25 wherein said refractory
metal-nitrogen-boron layer is tungsten-nitrogen-boron.
27. The interconnect device of claim 25 wherein said conductive
layer is copper.
28. A MIM structured capacitor comprising: (a) a substrate having a
dielectric layer thereon and having a storage node communicating
through a portion of the substrate, wherein the dielectric layer
has a via hole therein and wherein a top surface of the storage
node communicates with the via hole; (b) a refractory
metal-nitrogen-boron layer deposited on the substrate; (c) a high
dielectric constant insulator layer deposited on the substrate
overlying the refractory metal-nitrogen-boron layer; and (d) an
upper electrode layer on said substrate overlying the refractory
metal-nitrogen-boron layer, the upper electrode layer filling said
via holes.
29. The MIM structured capacitor of claim 28 wherein the substrate
is silicon.
30. The MIM structured capacitor of claim 28 wherein the dielectric
layer is silicon dioxide.
31. The MIM structured capacitor of claim 28 wherein the high
dielectric constant insulator layer is tantalum dioxide.
32. The MIM structured capacitor of claim 28 wherein the upper
electrode layer is titanium nitride.
33. A barrier film for use in the fabrication of wafers comprising:
a ternary phase comprising tungsten nitride and tungsten
boride.
34. The barrier film of claim 33 wherein the atomic percentage of
nitrogen is between about 2.5% and about 15%.
35. The barrier of film of claim 40 wherein the atomic percentage
of boron is about 20%.
36. A barrier film for use in the fabrication of wafer comprising:
a surface layer comprising tungsten nitride and boron nitride; and
a lower layer comprising tungsten boride and tungsten nitride.
37. The barrier film of claim 36 wherein said surface layer is
about 7.5 nm thick.
38. The barrier film of claim 36 wherein the atomic percentage of
nitrogen in said surface layer is between about 40% and 18%.
39. The barrier film of claim 36 wherein the atomic percentage of
nitrogen in said lower layer is between about 5% and 18%.
40. The barrier film of claim 36 wherein the atomic percentage of
boron in said surface layer is between about 10% and 20%.
41. The barrier film of claim 36 wherein the atomic percentage of
boron is said lower layer is between about 20% and 25%.
42. A barrier film for use in the fabrication of wafer comprising:
a surface layer consisting essentially of tungsten, boron and
nitrogen; and a lower layer consisting essentially of tungsten,
boron and nitrogen.
43. The barrier film of claim 42 wherein said surface layer is
about 7.5 nm thick.
44. The barrier film of claim 42 wherein the atomic percentage of
nitrogen in said surface layer is between about 40% and 18%.
45. The barrier film of claim 42 wherein the atomic percentage of
nitrogen in said lower layer is between about 5% and 18%.
46. The barrier film of claim 42 wherein the atomic percentage of
boron in said surface layer is between about 10% and 20%.
47. The barrier film of claim 42 wherein the atomic percentage of
boron is said lower layer is between about 20% and 25%.
48. A barrier film for use in the fabrication of wafers comprising:
a ternary phase consisting essentially of tungsten, nitrogen, and
boron.
49. The barrier film of claim 48 wherein the atomic percentage of
nitrogen is between about 2.5% and about 15%.
50. The barrier of film of claim 48 wherein the atomic percentage
of boron is about 20%.
Description
[0001] This application claims priority from U.S. Provisional
Application Serial No. 60/384,641 filed May 31, 2002 entitled,
"Metal Nitride Formation". The foregoing patent application, which
is assigned to the assignee of the present application, is
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] Refractory metal-based binary and ternary layers have been
investigated as promising candidates for use in barrier layers in
the fabrication of interconnect structures in integrated circuits.
Barrier layers are used to prevent diffusion between the conductive
(metallized) and dielectric layers of interconnect metallization
structures, as such diffusion would degrade the planned and
controlled electrical access (e.g., via holes) between successive
conductive layers. Barrier layers are preferably highly amorphous
as grain boundaries in polycrystalline (i.e., non-amorphous)
barrier films provide pathways for diffusion, such as diffusion of
copper in copper metallization structures. A major goal in the
formation of refractory metal-based binary and ternary films is,
therefore, maintenance of the films' amorphous character.
[0003] Because barrier films may be deposited as an intermediary
step in integrated circuit fabrication and because subsequent
processing may involve temperatures of up to 800.degree. C., it is
important that the barrier films retain their amorphous character
following exposure to high temperatures. It is also desirable that
barrier films possess low resistivity, as net line resistance
following complete line encapsulation should be minimized. In
addition, increasing aspect ratios of interconnect structures
require barrier layers with good conformal step coverage. Finally,
it is also important to minimize microscopic reactions between the
barrier layer and the adjoining layers.
[0004] Refractory metal-based binary and ternary layers have also
been investigated for use in bottom electrode applications of
metal-insulator-metal (MIM) structured capacitors in dynamic random
access memory (DRAM) fabrication. One important consideration for
choosing a material for a bottom electrode is that it be inert when
exposed to oxygen during the high temperature deposition of the
dielectric layer and in the post-deposition annealing in an oxygen
ambient, as such conditions are necessary to achieve a high
dielectric constant and low leakage current in the capacitor
structure. In addition to this, it is important that the material
chosen allow for uniform film coverage on highly aggressive
geometries.
[0005] Metal nitride films deposited by conventional methods such
as chemical vapor deposition recrystallize at annealing
temperatures above 500.degree. C. with thermal desorption of
nitrogen, decreasing the value of such films as barrier layers.
Yet, atomic layer deposition of tungsten nitride utilizing a gas
phase reaction between WF.sub.6 an NH.sub.3 results in a film with
a resistivity of about 4500 milli-ohms, thereby diminishing the
value of such films for use as a capacitor electrode.
[0006] As an example of refractory metal deposition, tungsten (W)
films have also been formed by the vapor phase reaction of WF6 and
B2H6 (referred to herein as ALD-W films). It should be understood
that atomic layer deposition (ALD) films may be formed using
refractory metals other than tungsten, such as tantalum,
molybdenum, titanium, zirconium, hafnium, cobalt, ruthenium,
platinum, iridium and palladium. ALD-W films are very good
candidates for use as barriers in copper metallization structures
and as bottom electrodes in MIM structured capacitors.
Nevertheless, certain problems are presented by ALD-W films.
Specifically, compounds having boron and oxygen only, such as boron
oxides, and metal compounds having B.sub.4O.sub.7, such as
CaB.sub.4O.sub.7 and NaB.sub.4O.sub.7, i.e., borates, are present
on the surface of ALD-W films following film deposition.
Furthermore, desorption and outgassing of unbound atomic components
of the ALD-W film can result in formation of contaminants and
undesirable changes in properties of the device.
[0007] Therefore, a need exists in the art for formation of a
reliable barrier layer having the properties of amorphous phase
following exposure to high temperatures and low resistivity. There
is a further need for a metal film for use as a bottom electrode in
MIM capacitors which: (1) is inert to oxidation during exposure to
high temperatures; (2) provides highly conformal step coverage on
highly aggressive geometries; and (3) has low resistivity.
SUMMARY OF THE INVENTION
[0008] The present invention provides a process for the treatment
of ALD films, or layers, such that the ALD film retains its
amorphous character but is modified to eliminate pre-existing
surface oxides and to prevent desorption and outgassing of unbound
atomic species during high temperature annealing.
[0009] In one embodiment of the process, a refractory metal-boron
layer is annealed in a nitrogen-containing environment at a
temperature of at least 400.degree. C., where the resulting
amorphous film comprises a single regime containing metal-nitrogen
bonds and metal-boron bonds. In an alternative embodiment of the
present invention, a refractory metal-boron layer is annealed in
nitrogen-containing ambient at temperatures >600.degree. C. The
resulting amorphous film comprises two regimes: (1) a surface layer
which is a nitrogen-rich ternary phase containing large amounts of
boron-nitrogen bonds and metal-nitrogen bonds as well as smaller
amounts of metal-boron and metal-nitrogen bonds; and (2) a
non-surface nitrogen-depleted ternary phase containing primarily
metal-boron and metal-nitrogen bonds. In a preferred embodiment,
the refractory metal is tungsten.
[0010] The layers resulting from the nitrogen-containing annealing
treatments are compatible with integrated circuit fabrication
processes. In one integrated circuit fabrication process, the
treated ALD-metal film is used as a barrier layer in copper (Cu)
metallization structures. In another integrated circuit fabrication
process, an ammonia ambient annealed ALD-metal film is used as a
bottom electrode for MIM structured capacitor DRAM.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0012] FIG. 1 depicts a schematic illustration of an apparatus that
can be used for the practice of the thermal annealing in reactive
nitrogen-containing gas embodiment described herein;
[0013] FIGS. 2a-2d depict schematic cross-sectional views of an
integrated circuit structure at different stages of integrated
circuit fabrication incorporating an ammonia ambient annealed ALD-W
film;
[0014] FIGS. 3a-3g depict schematic cross-sectional views of an
integrated circuit during different stages of MIM capacitor
fabrication incorporating the process of the present invention;
[0015] FIG. 4a illustrates an x-ray diffraction pattern of an ALD-W
film prior to treatment using the process of the present
invention;
[0016] FIG. 4b illustrates an x-ray diffraction pattern of an ALD-W
film following treatment according to the process of the present
invention;
[0017] FIG. 5 illustrates a transmission electron microscopy (TEM)
image of a cross section of a substrate-glue layer-ALD-W film
structure following treatment in accordance with the present
invention;
[0018] FIG. 6 shows sheet resistance variation of ALD-W versus
W--B--N films as a function of annealing temperature;
[0019] FIGS. 7a and 7b show the binding energy shifts of tungsten
(W(4f)), and boron (B(1s)), respectively, of an untreated,
unannealed ALD-W film following argon sputtering with spectra taken
at 5 second intervals from 0 seconds to 20 seconds;
[0020] FIGS. 8a-8c show the binding energy shifts of tungsten
(W(4f)), nitrogen N(1s) and boron (B(1s)), respectively, of the
ALD-W film following annealing at 500.degree. C. in ammonia ambient
for 60 seconds with XPS spectra taken at 5 second intervals of
argon sputtering from 0 seconds to 25 seconds;
[0021] FIGS. 9a-9c show the binding energy shifts of tungsten
(W(4f)), nitrogen N(1s) and boron (B(1s)), respectively, of the
ALD-W film following annealing at 700.degree. C. in ammonia ambient
for 60 seconds with XPS spectra taken at 10 second intervals from 0
seconds to 60 seconds; and
[0022] FIG. 10a illustrates the distribution of atoms of an ALD-W
film compared to the distribution of atoms of an ALD-W film
following ammonia ambient annealing at 700.degree. C. as a function
of sputtering time; and FIG. 10b shows a comparison of the nitrogen
content as a function of sputtering time between the ALD-W film
annealed at 500.degree. C. in ammonia and ALD-W film annealed at
700.degree. C. in ammonia.
DETAILED DESCRIPTION OF THE INVENTION
[0023] FIG. 1 shows a schematic representation of a wafer
processing system 10 that can be used to perform the
nitrogen-containing gas ambient thermal annealing process described
herein. Referring to FIG. 1, the CVD system 10 includes reactor
chamber 30, which receives gases from a gas delivery system 89 via
gas lines 92A-C (other lines may be present but not shown). A
vacuum system 88 is used to maintain a specified pressure in the
chamber and removes gaseous byproducts and spent gases from the
chamber. An RF power supply 5 provides radio-frequency power to the
chamber for plasma-enhanced processes. A liquid heat exchange
system 6 employs a liquid heat exchange medium, such as water or a
water-glycol mixture, to remove heat from the reactor chamber and
maintain certain portions of the chamber at a suitable temperature
for stable process temperatures. A processor 85 controls the
operation of the chamber and sub-systems according to instructions
stored in memory 86 via control lines 3, 3A-D (only some of which
are shown).
[0024] Processor 85 executes system control software, which is a
computer program stored in a memory 86 coupled to processor 85.
Preferably, memory 86 may be a hard disk drive, but memory 86 may
be other kinds of memory. In addition to a hard disk drive (e.g.,
memory 86), CVD apparatus 10 in a preferred embodiment includes a
floppy disk drive and a card rack. Processor 85 operates under the
control of the system control software, which includes sets of
instructions that dictate the timing, mixture of gases, gas flow,
chamber pressure, chamber temperature, RF power levels, heater
pedestal position, heater temperature and other parameters of a
particular process. Other computer programs such as those stored on
other memory including, for example, a floppy disk or other
computer program product inserted in a disk drive or other
appropriate drive, may also be used to operate processor 85.
[0025] Gas delivery system 89 includes gas supply panel 90 and gas
or liquid or solid sources 91A-C (additional sources may be added
if desired), containing gases, liquids, or solids that vary
depending on the desired processes used for a particular
application. Generally, the supply line for each of the process
gases includes a shut-off valve (not shown) that can be used to
automatically or manually shut off the flow of process gas, as well
as a mass flow controller (not shown) that measures the flow of gas
or liquid through each of the supply lines. The rate at which the
process and carrier gases and/or other dopant or reactant sources
are supplied to reaction chamber 30 also is controlled by
temperature-based liquid or gas mass flow controllers (MFCs) (not
shown) and/or by valves (not shown). Of course, it is recognized
that other compounds may be used as deposition and clean sources.
In alternative embodiments, the rate at which the process and
carrier gases are supplied to reaction chamber 30 also may be
controlled by a pressure-based fixed or variable aperture. When
toxic gases are used in the process, the several shut-off valves
may be positioned on each gas supply line in conventional
configurations. Gas supply panel 90 has a mixing system which
receives the deposition process and carrier gases (or vaporized
liquids) from the sources 91A-C for mixing and sending to a central
gas inlet 44 in a gas feed cover plate 45 via supply lines 92A-C.
The mixing system, the input manifold to the mixing system, and the
output manifold from the mixing system to the central inlet 44 may
be made of nickel or of a material such as alumina plated with
nickel.
[0026] When a liquid source is used, there are many different ways
to introduce a source gas using a liquid source in a CVD system.
One way is to confine and heat the liquid in an ampule so that the
vapor pressure provides a stable flow of the vaporized source that
is sufficient for the deposition process. The ampule is typically
not filled with liquid, but has a "head space" over the liquid,
acting as a vapor reservoir. Because the vapor pressure depends on
the temperature of the liquid, precise temperature control of the
liquid source is important. A mass flow controller (MFC) may be
used to control the output of the source gas to the chamber.
[0027] Another way to introduce a source gas using a liquid source
is to bubble a carrier gas, such as helium, through the liquid. The
carrier gas provides a head pressure over the liquid and carries
the vapor downstream to the chamber. The liquid may be
temperature-controlled to maintain a constant vapor partial
pressure. It is desirable to heat the liquid above the highest
expected ambient temperature of the environment in which the ampule
is located, so that a constant temperature may be maintained using
only a heater. As discussed above, a MFC may be used to control the
carrier gas/vapor mixture to the chamber. As an alternative to
using an MFC, which operates on a principle of thermal mass
transfer and is typically calibrated to a particular gas, a
pressure-regulating device may be used to control the output of the
source gas to the chamber. One such device is an aperture, or
orifice, that acts to throttle the gas flow and hence allows a
higher pressure to be maintained on one side of the orifice than
the other. By controlling the chamber (output) pressure, bubbler
gas flow, and liquid temperature, a fixed orifice may maintain a
constant pressure over the liquid and hence a constant vapor
concentration in the source gas. As a variation of this technique,
an additional gas source, such as argon, that provides relatively
small volumes of gas to the head space over the liquid may be
utilized to maintain the head pressure despite other changes, such
as the temperature of the liquid, for example. This pressurizing
gas may be used with sources incorporating either an MFC or orifice
on the source output.
[0028] In other embodiments, the gas mixing system may include a
liquid injection system to provide a source gas from a vaporized
liquid source into the chamber. A liquid injection system vaporizes
a measured quantity of liquid into a carrier gas stream. Because
this type of system does not depend on the vapor pressure of the
liquid for operation, the liquid does not need to be heated. A
liquid injection system is preferred in some instances as it
provides greater control of the volume of reactant liquid
introduced into the gas mixing system compared to bubbler-type
sources.
[0029] Liquid heat exchange system 6 delivers liquid to various
components of chamber 30 to maintain these components at a suitable
temperature during the high temperature processing. This system 6
acts to decrease the temperature of some of these chamber
components in order to minimize undesired deposition onto these
components due to the high temperature processes. As seen in FIG.
1A, heat exchange passages 79 within gas feed cover plate 45 allow
the heat exchange liquid to circulate through gas feed cover plate
45, thus maintaining the temperature of gas feed cover plate 45 and
adjacent components. Liquid heat exchange system 6 includes
connections (not shown) that supply the liquid (such as water)
through a heat exchange liquid manifold (not shown) for delivering
the liquid to the gas distribution system including faceplate 40
(discussed below). A waterflow detector detects the waterflow from
a heat exchanger (not shown) to the enclosure assembly.
[0030] A resistively-heated pedestal 32 supports wafer 36 in a
wafer pocket 34. Pedestal 32 may be moved vertically between
processing positions and a lower loading position using a
self-adjusting lift mechanism. Lift pins 38 are slidable within
pedestal 32 but are kept from falling out by conical heads on their
upper ends. The lower ends of lift pins 38 may be engaged with a
vertically movable lifting ring 39 and thus can be lifted above the
pedestal's surface. With pedestal 32 in the lower loading position
(slightly lower than an insertion/removal opening 56), a robot
blade (not shown) in cooperation with the lift pins and the lifting
ring transfers wafer 36 in and out of chamber 30 through
insertion/removal opening 56, which can be vacuum-sealed to prevent
the flow of gas into or out of the chamber through
insertion/removal opening 56. Lift pins 38 raise an inserted wafer
(not shown) off the robot blade, and then the pedestal rises to
raise the wafer off the lift pins onto the wafer pocket on the
upper surface of the pedestal.
[0031] Through the use of the self-aligning lift mechanism,
pedestal 32 then further raises wafer 36 into the processing
position, which is in close proximity to a gas distribution
faceplate (hereinafter "showerhead") 40. The process gas is
injected into reactor 30 through central gas inlet 44 in gas-feed
cover plate 45 to a first disk-shaped space 48 and from thence
through passageways 57 in a baffle plate (or gas blocker plate) 62
to a second disk-shaped space 54 to showerhead 40. Showerhead 40
includes a large number of holes or passageways 42 for jetting the
process gas into process zone 58.
[0032] The process gas jets from holes 42 in showerhead 40 into
processing zone 58 between the showerhead and the pedestal, so as
to react at the surface of wafer 36. The process gas byproducts
then flow radially outward across the edge of wafer 36 and a flow
restrictor ring 46 (described in more detail below), which is
disposed on the upper periphery of pedestal 32 when pedestal 32 is
in the processing position. Next, the process gas flows through
choke aperture formed between the bottom of annular isolator 52 and
the top of chamber wall liner assembly 53 into pumping channel 60.
Upon entering pumping channel 60, the exhaust gas is routed around
the perimeter of the process chamber, to be evacuated by the vacuum
pump 82. Pumping channel 60 is connected through exhaust aperture
74 to pumping plenum 76. Exhaust aperture 74 restricts the flow
between the pumping channel and the pumping plenum. Valve 78 gates
the exhaust through exhaust vent 80 to vacuum pump 82. Throttle
valve 83 is controlled by the system controller (not shown in this
view) according to a pressure control program stored in memory (not
shown) which compares a measured signal from a pressure sensor (not
shown), such as a manometer, against a desired value which is
stored in memory or generated according to the control program.
[0033] The sides of annular pumping channel 60 generally are
defined by ceramic ring 64, a chamber lid liner 70, a chamber wall
liner 72, and an isolator 52. Chamber lid liner 70 is placed on the
side of pumping channel 60 facing a lid rim 66 and conforms to the
shape of the lid. Chamber wall liner 72 is placed on the side of
pumping channel 60 facing main chamber body 11. Both liners are
preferably made of a metal, such as aluminum, and may be bead
blasted to increase the adhesion of any film deposited thereon. Lid
and wall chamber liners 70 and 72 are sized as a set. Chamber lid
liner 70 is detachably fixed to lid rim 66 by a plurality of pins
that also electrically connect the lid liner to the lid rim.
However, chamber wall liner 72 is supported on a ledge formed on
the outer top of ceramic ring 64 and is precisely formed to have a
diameter such that a radial gap is formed between chamber wall
liner 72 and main chamber body 11, and so that an axial gap is
formed between the lid and chamber liners.
[0034] Choke aperture 50 has a substantially smaller width than the
depth of the processing zone 58 between showerhead 40 and wafer 36,
and is substantially smaller than the minimum lateral dimensions of
circumferential pumping channel 60, for example by at least a
factor of five. The width of the choke aperture is made small
enough, and its length long enough, so as to create sufficient
aerodynamic resistance at the operating pressure and gas flow so
that the pressure drop across choke aperture is substantially
larger than any pressure drops across the radius of the wafer or
around the circumference of the annular pumping channel. The
constricted exhaust aperture performs a function similar to that of
the choke aperture by creating an aerodynamic impedance, creating a
nearly uniform pressure around circumferential pumping channel
60.
[0035] Motors and optical sensors (not shown) are used to move and
determine the position of movable mechanical assemblies such as
throttle valve 83 and pedestal 32. Bellows (not shown) attached to
the bottom of pedestal 32 and chamber body 11 form a movable
gas-tight seal around the pedestal. The pedestal lift system,
motors, gate valve, plasma system, including an optional remote
plasma system 4 (which may be used to provide chamber clean
capability using a remote plasma formed using, for example, a
microwave source), and other system components are controlled by
processor 85 over control lines 3 and 3A-D, of which only some are
shown.
[0036] Also seen is pedestal 32, liners 70 and 72, isolator 52,
ring 64, and pumping channel 60. This figure shows the flow of
processing gas out of nozzles 42 in showerhead 40 toward wafer 36,
then radially outward flow over wafer 36. Thereafter, the gas flow
is deflected upwardly over the top of restrictor ring 46 into
pumping channel 60. In pumping channel 60, the gas flows along
circumferential path 86 towards the vacuum pump.
[0037] Pumping channel 60 and its components are designed to
minimize the effects of unwanted film deposition by directing the
process gas and byproducts into the exhaust system. One approach to
reducing unwanted depositions uses purge gas to blanket critical
areas, such as ceramic parts and the heater edge and backside.
Another approach is to design the exhaust system to direct the flow
of reactive gas away from critical areas. The exhaust flow may form
"dead zones", where little gas movement occurs. These dead zones
approximate a purge gas blanket in that they displace reactive
gases in that area and reduce unwanted depositions.
[0038] The present invention inhibits unwanted deposition on the
pedestal and other parts of the chamber in other ways.
Specifically, the present invention utilizes flow restrictor ring
46 to minimize gas flow beyond the pedestal to the bottom of the
chamber. Flow restrictor ring 46 is supported by pedestal 32 during
processing, as mentioned above. When the pedestal is lowered for
wafer unloading and loading, the restrictor ring sits on ceramic
ring 64 in ledge 69. As the pedestal supporting the next wafer is
raised into processing position, it picks up the flow restrictor
ring. At the pressures used in the chamber for the titanium
processes according to embodiments of the invention, gravity is
sufficient to hold both the wafer (disposed in the wafer pocket)
and the restrictor ring on the pedestal.
[0039] Prior to operation of the nitrogen-ambient thermal annealing
process of the present invention, a refractory metal-boron layer is
deposited onto the surface of a partially formed integrated
circuit. The apparatus, method and conditions for depositing a
refractory metal-boron layer are described in commonly assigned
U.S. patent application Ser. No. 09/604,493, entitled "Formation of
Boride Barrier Layers Using Chemisorption Techniques", filed Jun.
27, 2000, which is incorporated herein by reference (Docket no.
4417). Referring to FIG. 2, a substrate 200 is shown. The substrate
may be any workpiece upon which film processing is performed.
Depending upon the stage of processing, the substrate 200 may be a
silicon substrate, or other material layer which has been formed on
a substrate surface. Substrate structure 250 is used generally to
denote the substrate 200 as well as other material layers formed on
the substrate 200. FIG. 2a, for example, shows a cross-sectional
view of a substrate structure 250, with a silicon substrate having
a material layer 202 deposited thereon. In accordance with one of
the preferred embodiments of the present invention, layer 202 may
be an oxide (e.g., silicon dioxide). The material layer 202 has
been conventionally formed and patterned to provide a contact hole
202H extending to the top surface 200T of substrate 200. One
skilled in the art will understand that the cross section and hole
pattern shown in FIG. 2a is only one of numerous possible
interconnect structures.
[0040] FIG. 2b shows a glue layer 204. In the present example,
MO-TiN was conventionally deposited over the substrate structure
250 to aid in the adhesion of a refractory metal-boron layer 208
which was deposited by atomic layer deposition. Deposition of glue
layer 204 is optional and the refractory metal-boron layer 208 may
be applied directly over substrate structure 250.
[0041] FIG. 2c shows the substrate structure 250 following thermal
annealing in ammonia at 700.degree. C. There is no additional layer
deposition. Rather, refractory metal-boron layer 208 has been
modified such that it is now a nitrogen-rich refractory metal-boron
layer 209.
[0042] FIG. 2d shows the substrate structure 250 following
formation of a contact layer 210 formed over the nitrogen-rich
refractory metal-boron layer 209. In the present example, contact
layer 210 is preferably made of copper (Cu), otherwise referred to
as copper metallization. Contact layer 210 may alternatively be
from the group of aluminum (Al), tungsten (W), or combinations
thereof. Contact layer 210 may be formed using electrochemical
plating (ECP), physical vapor deposition (PVD), or a combination of
both ECP and PVD. Contact layer 210 is preferably formed by copper
seeding using PVD followed by ECP.
[0043] The nitrogen-rich refractory metal-boron layer 209 is formed
by thermal annealing of the substrate structure 250 of FIG. 2b in a
nitrogen containing ambient at temperatures ranging from
400.degree. C. to 800.degree. C. for a period of 10 seconds to 100
seconds. In the preferred embodiment, refractory metal boron layer
208 is formed by the atomic layer deposition technique using
WF.sub.6 and B.sub.2H.sub.6, resulting in an ALD-W layer. In the
preferred embodiment, the nitrogen-containing gas is ammonia. The
resulting layer 209 is ternary, W--B--N. It will be understood by
one skilled in the art that other gas phase reactive
nitrogen-containing compounds, such as hydrazine (N.sub.2H.sub.4),
dimethyl hydrazine ((CH.sub.3).sub.2N.sub.2H.sub.2), other
derivatives of hydrazine and combinations thereof, may be used in
place of ammonia. The W--B--N layer 209 produced by the process of
the present invention remains amorphous following thermal
annealing.
[0044] In another embodiment, the process of the present invention
is used in the fabrication of an MIM capacitor. FIGS. 3a-3g
illustrate schematically cross-sectional views of an integrated
circuit during different stages of MIM capacitor fabrication. FIG.
3a illustrates a cross sectional view of a partially formed MIM
structured capacitor. A silicon substrate 300 having a storage node
310 is coated with a silicon dioxide (SiO.sub.2) material layer
320. Substrate structure 350 is used generally to denote the
substrate 300 as well as other material layers formed on the
substrate 300. The silicon dioxide material layer 320 has been
conventionally formed and patterned to provide a contact hole 320H
communicating with the top surface of storage node 310.
[0045] A glue layer 330, shown in FIG. 3b, is deposited by
conventional chemical vapor deposition methods over the surface of
the substrate structure 350. In the preferred embodiment, glue
layer 330 is composed of MO-TiN. Glue layer 330 is used to promote
the adhesion of the subsequent ALD-W layer and to ensure good
electrical contact with the top surface of storage node 310. As
shown in FIG. 3c, an ALD-W layer 340 is deposited over glue layer
330. ALD-W layer 340 is deposited by atomic layer deposition using
WF.sub.6 and B.sub.2H.sub.6. FIG. 3d illustrates the W--B--N layer
360 formed following nitrogen treatment of ALD-W layer 340 in
accordance with the process of the present invention and as
described in reference to FIGS. 1 and 2a through 2c.
[0046] As shown in FIG. 3e, the next step in the process of MIM
capacitor fabrication is planarization of W-N-B layer 360 and glue
layer 330 at the top of the structure by chemical-mechanical
polishing. As shown in FIG. 3f, the substrate structure is coated
with a high dielectric constant insulator layer 370 and the entire
substrate structure is then subjected to the thermal treatments. In
the preferred embodiment, high dielectric constant insulator layer
370 is Ta.sub.2O.sub.5 and the thermal treatments include: (1)
annealing at about 700.degree. C. for crystallization of the
insulator layer; and (2) treatment in oxygen ambient at about
500.degree. C. It will be understood by one of ordinary skill in
the art that other high dielectric constant insulator materials,
such as BST, may be used in lieu of Ta.sub.2O.sub.5 and that the
thermal treatments may or may not be conducted in the presence of
oxygen. As a final step in the fabrication of the MIM structured
capacitor, an appropriate upper electrode material 380 is deposited
by conventional means over the substrate structure 350. In the
preferred embodiment, the upper electrode material 380 is titanium
nitride (TiN) and is deposited by atomic layer deposition. It will
be understood that other conventional conductive materials may be
used as upper electrode material 380.
[0047] Embodiments of the present invention are further described
in reference to the examples discussed below.
EXAMPLE
[0048] Titanium nitride (TiN) deposited oxidized silicon substrates
were used to generate the data for this example. The TiN layer was
deposited by metal organic chemical vapor deposition using
tetrakismethylamino titanium (TDMAT) precursor treated with plasma.
A tungsten-boron film (ALD-W) was then deposited on each of the
sample wafers using the ALD process using tungsten hexafluoride
(WF.sub.6) and diborane (B.sub.2H.sub.6) as precursors, using a 30
second anneal in ammonia ambient at a fixed chamber pressure of 10
Torr. Temperatures ranged from 400.degree. C. to 700.degree. C.
[0049] Structural changes were characterized by glancing angle
x-ray diffraction using an incident angle of the x-ray source at
0.5 degrees with power for the x-ray source set at 45 kV and 40 mA.
FIG. 4a shows an x-ray diffraction spectrum of the ALD-W film as
deposited. The broad peaks indicate an amorphous structure. FIG. 4b
shows an x-ray diffraction spectrum of the W--B--N layer that has
been annealed at 700.degree. C. for 30 seconds in an NH.sub.3
ambient. The broad peaks indicate that the resulting W--B--N layer
remains amorphous. Moreover, the spectra from films annealed at
temperatures ranging from 400.degree. C. to 600.degree. C. have
identical x-ray diffraction spectra (data not shown).
[0050] FIG. 5a is a plane-view transmission electron microscope
image of the as-deposited film (x-ray diffraction spectra seen in
FIG. 4a). The electron diffraction patterns exhibit only a few
broad diffraction rings, indicating that the film has an amorphous
structure. The transmission electron microscope image does not show
a typical cluster boundary shown in amorphous films deposited by
CVD techniques, suggesting that the mechanism for ALD film
formation differs from that of CVD film formation.
[0051] FIG. 5b shows a cross-sectional view of a transmission
electron microscope image of an ALD-W film that has been annealed
at 700.degree. C. There is no detectable crystallization of the
film. Additionally, there is no interaction detected at the
ALD-W/MOTin interface.
[0052] Sheet resistances (RSTotal) of 50 nm WBN films deposited on
a TiN glue layer were measured by a four-point probe. In order to
monitor the effect of temperature on the sheet resistance fo the
WBN layer (Rs.sub.w), the following calculation was made:
1/Rs.sub.w=(1/RS.sub.Total)-(1/Rs.sub.TiN).
[0053] FIG. 6 illustrates the variation in sheet resistance of the
50 nm W--B--N films as a function of annealing temperature. The
sheet resistance of the WBN film as deposited with no thermal
treatment, referred to as ASD, is shown for comparison. An increase
in sheet resistance is observed as between the ASD sample (about 42
.OMEGA./sq) and the ammonia ambient 400.degree. C. sample (about 54
.OMEGA./sq). As annealing temperatures increase beyond 400.degree.
C., sheet resistance decreases, then levels for annealing
temperatures greater than 600.degree. C. (36 .OMEGA./sq). The
corresponding resistivities were determined to be 162, 142 and 107
.sub.u.OMEGA.-cm at annealing temperatures of 400.degree. C.,
500.degree. C., and >600.degree. C., respectively, demonstrating
that anneal temperatures affect film properties. The results
illustrate also the existence of two temperature regimes that
achieve different film structural characteristics: (1) annealing
temperatures between 400.degree. C. and 500.degree. C.; and (2)
annealing temperatures greater than 600.degree. C.
[0054] The chemical status of the film surfaces were examined by
x-ray photoelectron spectroscopy (XPS) using a monochromatic A1
K.alpha. source and a concentric hemispherical electron energy
analyzer. XPS depth profiling was used to determine the chemical
bonding configuration, and the atomic concentrations and
distributions as a function of depth within the films. To
characterize the binding energy shifts, the XPS database maintained
by the National Institute of Standards and Technology was used a
reference. Because the samples are exposed to air after ammonia
ambient annealing, XPS spectra were taken after every 5 or 10
seconds of Argon sputtering so that the effects of air exposure
could be disregarded.
[0055] FIG. 7 shows the binding energy shifts of tungsten W.sub.4f
(a), and boron B.sub.1s (b) of an untreated, unannealed ALD-W film
following argon sputtering with spectra taken at 5 second intervals
from 0 seconds to 20 seconds. FIG. 7a illustrates the XPS binding
energies associated with W.sub.4f.
[0056] The 0 second signal exhibits four peaks at 31.2, 33.3, 35.6
and 37.7 eV, where the first two peaks represent W(4f.sub.7/2) and
W(4f.sub.5/2) electrons for elemental tungsten in the zero
oxidation state, and the latter two peaks correspond to those for a
tungsten oxide. The tungsten oxide peaks disappear after 5 seconds
of argon sputtering and the XPS spectra reveals binding energies
identical to elemental tungsten with a weak satellite at 36.7 eV,
which represents W(5.sub.p3/2).
[0057] FIG. 7b shows the binding energy shifts of boron. At 0
seconds, a broad peak appears at 192.4 eV, which may indicate boron
oxide (B.sub.2O.sub.3) at the film surface. The peak at 192.4 eV
disappears after the first sputtering, however, and the signals in
the 5 second and subsequent time points line up at 187.9 eV. This
peak at 187.9 indicates that boron atoms exist in the film bound
chemically to tungsten (as tungsten boride WB.sub.x), quantified to
be at about 20 atomic percent (see FIG. 8a). XPS data on N.sub.1s
(not shown) revealed a broad peak at 402 eV, which may have been
due to nitrogen atoms incorporated into the tungsten oxide during
exposure to air.
[0058] FIG. 8 shows the binding energy shifts of tungsten W.sub.4f,
nitrogen N.sub.1 and boron B.sub.1s of an ALD-W film following
annealing at 500.degree. C. in an ammonia ambient for 60 seconds.
XPS spectra was taken at 5 second intervals of argon sputtering
from 0 seconds to 25 seconds. FIG. 8a indicates the existence of
tungsten oxide at the surface of the film. The tungsten oxide
disappears after the first 5 seconds of argon sputtering. FIG. 8b
indicates a peak at 397.1 eV indicating the formation of tungsten
nitride. FIG. 8c shows a peak at 187.9 eV indicating the presence
of boron atoms bound to tungsten. In summary, the W--N--B film
resulting from ammonia ambient annealing at 500.degree. C. (within
the lower temperature regime noted earlier) shows the nitrogen
atoms preferentially binding to tungsten.
[0059] FIG. 9 shows the binding energy shifts of tungsten W.sub.4f,
nitrogen N.sub.1s and boron B.sub.1s of an ALD-W film following
annealing at 700.degree. C. in ammonia ambient for 60 seconds. XPS
spectra was taken at 10 second intervals from 0 seconds to 60
seconds. FIG. 9a indicates the existence of a small amount of
tungsten oxide at the surface of the film. The tungsten oxide
disappears after the first 5 seconds of argon sputtering. FIG. 9a
further shows a 0.5 eV shift to a higher binding energy in each of
the W.sub.4f peaks, indicating a charge transfer from tungsten to
nitrogen. FIG. 9b does not indicate formation of a surface oxide,
suggesting that a pre-existing oxide formed at the surface during
air exposure is reduced during the higher temperature ammonia
ambient anneal and that possibly further oxidation after the
ammonia ambient anneal is prohibited by the presence of a surface
nitride. FIG. 9b further shows both tungsten nitride and boron
nitride peaks, with the tungsten nitride peak being the stronger of
the two.
[0060] FIG. 9c shows the formation of boron nitride with a peak
located at 190.7 eV. The boron nitride peak disappears however
after about 30 seconds of argon sputtering, corresponding to a film
depth of about 7.5 nm. Following 30 seconds of sputtering, the
boron signal shows the presence of tungsten-boron bonds.
[0061] To investigate the thermal desorption behavior of any boron
and/or nitrogen containing species, thermal desportion spectroscopy
(TDS) analysis was performed on the 700.degree. C. annealed sample.
It was expected that the TDS signals of the boron-containing
species would be close to those of nitrogen ions due to their
similar atomic mass unit values. The atomic mass unit of
boron-containing species, such as BH.sub.3 (m/e=13.8) and
B.sub.2H.sub.6 (m/e=27.6), are very close to those of single- and
double-charged nitrogen ions, such as N.sub.2.sup.+(m/e=28.0) and
N.sub.2.sup.2+(m/e=14.0). Therefore, if there are signals that
appear due to the desorption of nitrogen, BH.sub.3 or
B.sub.2H.sub.6 would have to show a simultaneous signal. Note that
neither BH.sub.3 nor B.sub.2H.sub.6 (thus, N.sub.2.sup.+ or
N.sub.2.sup.2+) show a signal (see FIG. 11).
[0062] FIG. 10a shows the atomic distribution of tungsten, nitrogen
and boron of the ALD-W film as a function of sputtering time before
and after annealing in ammonia ambient at 700.degree. C. for 60
seconds. Increased sputtering time corresponds with increased film
depth. In FIG. 10a, the shaded data points show the atomic
distribution for the untreated, unannealed ALD-W film, and the open
squares, circles and triangles show the atomic distribution for the
annealed ALD-W film. Note that initially a nitrogen-rich W--B--N
layer is formed, where later a nitrogen-depleted layer is
formed.
[0063] FIG. 10b compares the nitrogen content as a function of
sputtering time for a film annealed at 500.degree. C. in an ammonia
ambient with a film annealed at 700.degree. C. in an ammonia
ambient. As the annealing temperature increases, the nitrogen atom
diffusion depth and surface concentration increase.
[0064] The specific process conditions disclosed in the above
discussion are meant for illustrative purposes only. Other
combinations of process parameters such as substrate structure
cross sectional profiles, temperatures, film thicknesses, and times
may also be used in treating metal layers to form the
nitrogen-containing metal layers described herein.
[0065] The description and teaching herein includes reference to
and detailed description of certain preferred embodiments of the
present invention, those skilled in the art may devise other
embodiments which incorporate the teaching of the present
invention.
[0066] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *